This application is the US national phase of international application PCT/IB01/01297 filed May 15, 2001, which designated the US.
The present invention relates to a device for controlling the cooling flows of gas turbines.
As is known, gas turbines comprise a compressor, to which air is fed from the external environment so as to bring it up to pressure.
The air under pressure passes into a series of combustion chambers which terminate in a nozzle and into each of which an injector feeds fuel which is mixed with the air so as to form a combustible air mixture to be burned.
The turbine converts the enthalpy of the gases combusted in the aforementioned combustion chamber into mechanical energy available for a user.
The present invention refers, in particular, to the outlet zone of the gas turbine compressor.
By way of introduction of the technical problems solved by the present invention, it should be noted that the constant attempt to increase the efficiency of gas turbines is subject to the requirement for optimisation of all the flows inside the turbine engines.
In particular, the air supplied from the compression stages, since it has been produced with considerable expenditure in terms of the thermodynamic cycle, must be used as far as possible for combustion, instead of for cooling or confining functions which moreover are required in the most critical hot zones.
The problem which is posed in this context is therefore that of correct metering of this air in the various zones, taking into account that the amount of air required is variable depending on the operating conditions, the age and the degree of wear or soiling of the turbine engine, its components and the dimensional variations of the components during the transients.
In fact, in the event of an insufficient air flow, the consequences are, at best, a significant reduction in the life of the components with the possibility of blade failure and fires.
It is pointed out here, incidentally, that these factors may have a negative effect resulting in an increase in costs for users.
In order to understand more fully the technical problems involved in the present invention, reference should be made first of all to FIGS. 1 to 3, which show, respectively: a cross-sectional view of a gas turbine according to the prior art, denoted overall by the reference number 20; an enlarged view of the outlet zone of the compressor 21 of the gas turbine 20; and the conventional solution for controlling the cooling flows of the gas turbine 20 which may envisage fixed bores 22 in the body 50 of the inner barrel 23.
In greater detail, FIG. 1 shows a gas turbine 20 provided with a compressor 21 with which an inner barrel 23 and a load-bearing bolster 24 are associated; FIG. 1 also shows, among other things, the rotors 25 and 26 of the turbine 20.
Examining in greater detail FIG. 2, it is possible to see the casing 27 and the blades 28, forming part of the compressor 21, the outlet diffuser 29 of the compressor 21, the venting outlet 33 of the load-bearing bolster 24 and the air seals 30 and 31 of the inner barrel 23; FIG. 2 also shows a portion of the rotor 32.
The solutions currently used for correct metering of the air flows intended for cooling and sealing consist in the specific definition of orifices on the supply tubes/ducts and determination of the degree of play between rotating members and labyrinths formed in complementary stator components.
Orifices and labyrinths (see FIG. 3) are therefore interdependent from a design point of view and precisely determined during finalisation of the prototype, so that extreme situations and deviations in design can be safely handled.
This means that these adjustments and tolerances are therefore defined by the manufacturer during assembly.
However, the need for an increase in the efficiency of the machines on the part of customers has resulted in a reduction in the air flows to the absolute minimum necessary, with the application of seals which are increasingly efficientxe2x80x94often excessively soxe2x80x94with the serious risks mentioned above.
In particular, there has been a tendency to reduce the amount of air which escapes from the compressor 21 towards the innermost portions of the machine 20 (FIGS. 1-2), in particular in the zone located inside the inner barrel 22.
This air, passing through a first barrier of labyrinth seals, then escapes from the vent of the load-bearing bolster 24 of the compressor 21 and through the front interspace of the first turbine rotor, through the labyrinth formed with the angel wings on the shanks of the blades and the stationary seals mounted on the casing.
The function of this air is therefore that of providing a seal from the oil vapours in the bolster 24 and hot gases inside the turbine 20, cooling the turbine disk and removing the heat produced by means of ventilation friction inside the inner barrel 23.
Experience has shown that often, the compromise adopted between the need for an increase in efficiency and reliability of the machine, since there is no possibility for adjustment, has resulted in a sudden reduction in reliability of the machine.
An object of the present invention is therefore to provide a device for controlling the cooling flows of gas turbines which is able to allow the possibility of varying the air flow entering into the inner barrel, without the need for replacement of the latter.
More particularly, the invention aims to avoid any kind of disassembly of the most important components of the turbine engine, while allowing variation in the air flow into the inner barrel.
Another object of the invention is to provide a device for controlling the cooling flows of the gas turbines which allows adjustment which is customized and repeatable over time, by simply stopping the machine and performing simple operations involving the selection and replacement of suitable component parts.
A further final object of the invention is to provide a device for controlling the cooling flows of gas turbines which is advantageous from a cost point of view.
Last but not least, an object of the invention is to provide a device for controlling the cooling flows of gas turbines which is substantially safe and reliable.
These and other objects are achieved by a device for controlling the cooling flows of gas turbines, where the aforementioned gas turbine is provided with a compressor with which an inner barrel and a load-bearing bolster are associated, characterized in that it envisages the arrangement of a plurality of replaceable nozzles which have an internal bore with different diameters and which can be mounted in suitable holes formed in the substantially cylindrical body of the aforementioned inner barrel so as to allow a variation in the flow of air entering into the aforementioned inner barrel, by means of the selection and replacement of at least some of the aforementioned nozzles with other nozzles having an internal bore with suitable diameters.
According to a preferred embodiment of the present invention, each of the aforementioned nozzles has a threaded section able to engage with a corresponding internally threaded section present in a hole formed in the aforementioned inner barrel.
According to a further preferred embodiment of the present invention, each replaceable nozzle has a cylindrical section with a diameter smaller than that of the threaded section and a pair of incisions for engagement with a magnetic-head spanner.
According to another preferred-embodiment of the present invention, the nozzles are inserted by means of a guide tube and a magnetic-head spanner, the guide tube being inserted inside a corresponding hole present in the casing of the aforementioned compressor.
More particularly, the guide tube has a threaded collar for allowing engagement thereof with a corresponding hole present in the casing of the compressor.
The guide tube is inserted into the hole of the compressor casing by sliding it until the aforementioned threaded collar thereof is screwed into the corresponding threading of the compressor casing with its end inside the machine making contact with the aforementioned inner barrel, so as to form a retaining and guiding channel inside which the nozzles to be screwed into the body of the inner barrel can be passed.
According to yet another preferred embodiment of the present invention, during operation of the aforementioned gas turbine, the holes in the compressor casing are closed using bolts, or other similar closing devices, inserted in position after removal of the guide tubes.
The present invention relates, moreover, to the fact that, in order to fix the nozzles in the operating position, it is further envisaged using a dimpling punch, which is used by employing the guide tube as a guide for the striking point.
Further characteristic features of the invention are defined in the claims accompanying the present patent application.